If you're not on Azure PaaS, these might help:
The error:
Server Error in '/' Application.
Could not load file or assembly 'ChilkatDotNet47' or one of its dependencies. An attempt was made to load a program with an incorrect format.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.BadImageFormatException: Could not load file or assembly 'ChilkatDotNet47' or one of its dependencies. An attempt was made to load a program with an incorrect format.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Assembly Load Trace: The following information can be helpful to determine why the assembly 'ChilkatDotNet47' could not be loaded.
WRN: Assembly binding logging is turned OFF.
To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1.
Note: There is some performance penalty associated with assembly bind failure logging.
To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog].
Stack Trace:
[BadImageFormatException: Could not load file or assembly 'ChilkatDotNet47' or one of its dependencies. An attempt was made to load a program with an incorrect format.]
System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +0
System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +37
System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +159
System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean forIntrospection) +80
System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +22
System.Reflection.Assembly.Load(String assemblyString) +29
System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +38
[ConfigurationErrorsException: Could not load file or assembly 'ChilkatDotNet47' or one of its dependencies. An attempt was made to load a program with an incorrect format.]
System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +724
System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory() +196
System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +45
System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +172
System.Web.Compilation.BuildManager.GetPreStartInitMethodsFromReferencedAssemblies() +91
System.Web.Compilation.BuildManager.CallPreStartInitMethods(String preStartInitListPath, Boolean& isRefAssemblyLoaded) +111
System.Web.Compilation.BuildManager.ExecutePreAppStart() +156
System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException) +695
[HttpException (0x80004005): Could not load file or assembly 'ChilkatDotNet47' or one of its dependencies. An attempt was made to load a program with an incorrect format.]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +660
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +89
System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +189
(This might also be relevant for ChilkatDotNet45, ChilkatDotNet46 and other versions).